Telephone-exchange system.



PATBNTED NOV. 15, 1904.

E. e. WEBSTER.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED FEB.14 1903.

N0 MODEL.

UNITED STATES Patented November 15, 1904.

PATENT OEEicE.

HARRY G. IVEBSTER, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE STROM-BERG-CARLSON TELEPHONE MANUFACTURING- COMPANY, OF ROCHES- TER, NEIVYORK, A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

SPECIFICATION forming part of Letters Patent No. 775,229, dated November15, 1904.

Application filed February 14, 1903- Serial No. 143,307. No model.)

To (Ml whom it Hilly/011116776:

Be it known that I, HARRY G. \Vnesrna, a citizen of the United States,residing at Chicago, in the county of Cook and State of Illinois, haveinvented a certain new and useful Improvement in Telephone ExchangeSystems, of which the following is a full, clear, concise, and exactdescription, reference be ing had to the accompanying drawing, forming apart of this specification.

My invention relates to telephonc-exchange systems, and moreparticularly to systems in which a common source of energy is located atthe central station to supply talking-current tosubstation-transmitters.

My invention is particularly useful in conjunction with systemsemploying a so-called differential cut-ofi' relay, by means of which theuse of the operators cord-circuit at the central station controls theline-signal to cause the extinction thereof upon the connection of cordconnecting apparatus with a subscribers telephone-line.

The objects of my invention are to provide a system in which theapparatus employed may serve the double purpose of regulating andcontrolling the voice-currents transmitted from one line'to another andat the same time to effect the operation of suitable line andsupervisory signals. I provide a system in which current for thesubstation-transmitters may be supplied entirely through linecircuitapparatus, as distinguished from those systems in which the substationtransmittercurrent is supplied wholly or partially through cord-circuitapparatus.

My invention provides an improvement over other systems, in which thenecessaryimpedance in the circuit supplying talking-current to thesubstation-transmitters is introduced by the provision of coils wound oniron cores on which there are short-circuited windings. Theseshort-circuited windings tend to decrease the impedance.

In my improved system the impedance-coils are on the line and cut-offrelays and serve other useful purposes in addition to that of providingthe necessary impedance. The linecircuit arranged in accordance with myinvention is adapted for use with instruments and connecting devices inwhich an alternating calling-current may be sent through a callbell at asubstation over either the tip or the sleeve side of the telephone-line.

An improved ringing-circuit is one of the principal features of myinvention.

The cord-circuit used in conjunction with my improved line-circuit may,if desired, be provided with two ringing'keys to correspond with linessome of which are operated with a calling-circuit over the sleeve sideof the line and others in which there is a calling-circuit over the tipside of the line. Since the tall:- ing-current is supplied to thesubstation-transmitters through line-circuit apparatus rather thanthrough the cord-circuit, itis possible to provide supervisory relays inthe cord-circuit which are wound to comymratively high resistanceforinstance, live hundred ohms whereby the operation of the supervisorysignaling devices is made more sensitive and reliable.

In accordance with my invention 1 provide at the central station asuitable common battery, to the terminals of which are connected twolimbs of a telephone-line leading to a substation. One of these limbsincludes in its circuit the two differential windings of a cutoff relayand one winding of a line-relay. The other limb includes in its circuita second cumulative winding of the line-relay. A 10- cal circuit jointlycontrolled by said line and cut-off relays affords current adapted toilluminate a line signaling-lamp. It will be apparent to those skilledin the art thatany other suitable form of line-signal may be employed inplace of the well-known lamp and local circuit described herein. Cordconnecting apparatus is provided for connecting lines for conversation,means being provided whereby the insertion of the plug of the cordconnecting apparatus within a line-jack causes the closure ofalow-resistance circuit through one winding of said cut-ofi' relay,whereby the same is given a net energization, and consequently actuatedto discontinue or prevent the illumination of the line signal-lamp. Asupervisory controlling-relay is provided and arranged to connect onebattery-pole with suitable supervisory signaling apparatus upon theinsertion of a plug of the cord-circuit within a line-jack.

My invention will be better understood by reference to the accompanyingdrawing, in which are illustrated at each of the substations A and Bcommon-battery telephone sets, comprising in each instance a switch-hook1,

serving when in its normal depressed position to connect the line-limb2, through a condenser 3 and call-bell 4, with the ground. When relievedof the weight of the receiver 5, the switch-hook assumes its alternativeupper position in which the line-limb 6 is connected, through thetransmitter 7 and primary winding 8 of the induction-coil, with thelinelimb 2. The secondary coil 9 of the induction-coil is connected withthe receiver 5. The limbs 2 and 6 lead to the central station C, wherethey are connected with the terminals of the common battery 10, whosepositive terminal is grounded, as shown. The limb 6 includes in itscircuit the two difierential windings 11 and 12 of a differentialcut-off relay 13 and a winding 14 of the line-relay 15. I have found itdesirable to make each of the differential cut-ofi relay-windings 11 and12 about one hundred ohms resistance and that of the winding 14 of theline-relay 15 of about one hundred ohms resistance. The limb 2 of thetelephone-line is connected, through a twohundred-ohm winding 16 of theline-relay 15. The windings 1 1 and 16 of the line-relay are madecumulative in their efl'ects upon the relay-core.

The armature 17 of the line-relay and the armature 18 of the cut-offrelay are included in a local circuit through a line signaling-lamp 19.The cut-off relay is provided with a second armature 20, adapted when inits attracted position to close a low-resistance circuit in shunt of thewinding 11 of the cut-ofl relay. The telephone-lines are each associatedwith an answering-jack 21 and calling-jacks 22, the tip-contacts 23 ofwhich are permanently connected to the limb 2 of the line, as shown. Thesleeve-contacts, which may be in the shape of thimbles 24., areconnected in parallel with the common terminal of the two windings 11and 12 of the cut-off relay.

1 have illustrated cord connecting apparatus having an answering-plug 25and a callingplug 26, the tip-contacts of which are connected by thetip-strand 27 and the sleevecontacts of which are connected by thesleevestrand 27, the continuity of the tip-strand being interrupted bythe condenser 28. The usual listening-hey 29 is provided, adapted whenmanipulated to connect the operators telephone set 30 in bridge of thecord-circuit.

In the present embodiment of my invention I have shown two ringing-keys31 and 32, the I ringing-key 31 serving when manipulated to connect thegenerator 33 between the ground and the sleeve-strand leading to thesleevecontact of the calling-plug 26, while a manipulation of theringing-key 32 serves to connect the generator 34 between the ground andthe tip-contact of the calling-plug 26. A supervisory controlling-relay35 is connected between the grounded side of the common battery 10 andthe sleeve-strand 27 of the cord-circuit. An attraction of the armature36 serves to connect the positive terminal of the battery 10 with oneterminal of each of the supervisory signalinglamps 37 and 38, whosecircuits are further controlled by the armatures 39 and 10 of thesupervisory relays .1 and 12, the relay 11 being connected in a circuitbetween the positive side of the battery 10 and the section of thetip-strand 27 of the cord-circuit leading to the tip-contact of theanswering-plug and the supervisory relay 12- being connected in acircuit between the positive side of the battery 10 and a contact 13,which normally makes connection with the portion of the tip-strand 27leading to the callingplug 26. An impedance-coil 14 is connected in apath between the contact of the listening-key and the negative pole ofthe battery 10. A condenser 16 is connected in the operatorstelephone-circuit between the contacts of the listening-key.

The operation of my improved system will now become apparent. Asubscriber at substation A upon removing the receiver 5 from itsswitch-hook 1 closes a circuit between the limbs 2 and 6 of theassociated telephone-line.

IOC

A circuit is thereby closed from the positive side of the battery 10through the winding 16 of the line-relay, through the transmitter andprimary winding 8, through the linelimb 6, the differential windings 11and 12 of the cut-01f relay 13, and the winding 14: of the line-relay 15to the negative pole of the battery 10. Current flowing over thiscircuit causes no net energization of the cut-off relay on account ofthe ditferential relation of the windings 11 and 12. The windings of theline-relay, however, are cumulative in their effects, and the line-relayis therefore actuated to cause the attraction of its armature 17. Thearmature 18 of the cut-off relay being in its normal unattractedposition, a circuit is thereby closed through the line signalinglamp 19to illuminate the same. The operator is thereby given a signal, to whichshe responds by the insertion of an answering-plug 25 of a cord-circuitwithin the answering-jack 21, associated with the callingtelephone-line. The insertion of the answering-plug within theanswering-jack closes the following circuit: from the positive pole ofthe battery 10, through the supervisory controlling-relay 35, to thesleeve-strand 27 of the cord-circuit, to the sleeve-contact 2 1 of theanswering-jack, through the winding 12 of the cut-off relay and thewinding ii of theline-relay, to thenegative ing substation, causes acurrent to tlow, side of the batteryll). The differential ett'ects ot'the windings 11 and 12 of the cut-oti' relay are thereby unbalanced andthe relay-core is 5 given a net energization due to the excess currentflowing through the coil 12 over that flowing through the coil 11. Thecutoff-relay armatures are therefore attracted, the armature 18 servingto break the local circuit through the line signal-lamp 19 and thearmature 20 serving to connect a low-resistance circuit in shunt of thewinding 11 ot' the cutotl relay. At the same time the currenti'lowingthrough the supervisory controlling-relay causes the attraction of itsarmature 36 to connect the positive pole of the battery 10 with thesupervisory signal-lamps 37 and 38.

A circuit through the supervisory relay *1 may be traced as follows:from the positive pole of the battery 10 to the tip-strand 27 of thecord-circuit, to the tip-contact 23 of the answering-jack 21, to theline-limb 2, through the switch-hook 1, the primary winding 8, thetransmitter T, the line-limb 6, the low-re sistance slumt-circuit aboutthe winding 11, the winding 12 ot' the cut-ott' relay, the winding ii ofthe line-relay, to the negative pole of the battery 10. The currentflowing through the supervisory relay a1 causes the attraction of thearmature 39 to break the otherwise completed circuit through thesupervisory signal-lamp 37. The circuit through the supervisorysignal-lamp 38 is completed by the armature it) of the supervisory relay4E2, which makes connection with its back contact, as shown. Theoperator manipulates her listening-key to connect her telephone set inbridge of the cord-circuit and ascertains the number of the subscribersstation with which the subscriber at substation A desires communication.Learning that substation B is desired, the operator inserts hercalling-plug 26 within a calling-jack 22, associated with the calledline to substation B. and thereupon manipulates her ringing-key 32 toconnect the generator 54: with the tip-strand of the cord-circuit. Theringing-circuit may be traced t'rom the tip-contact of the callingjack22 through the line-limb 2, the condenser the call-bell at, to theground, with which one terminal of the ringing-generator is connected.Manipulation of the ringing-key also serves to connect the sleeve-strand27, leading to the sleeve-contact ot' the callingplug 26, with theground.

The insertion of the calling-plug 26 within a calling-jack 22 closes thefollowing circuit: from the positive pole of the battery ll) through thesupervisory controlling-relay 35, the sleeve-strand of thecord-circuit,the sleevecontact 2% of the calling-jack 22, the winding 12of the cut-oti' relay, the winding 1* of the line-relay, to the negativepole of the battery ll). This circuit, similarly to that traced tor theapparatus associated with the callcausing the attraction ol thearmatures l7 and 1b, the armature 18 serving immediately to open thecircuit through the linelamp 19. The attraction of the armature 20 atonce closes the low-resistance shunt-path about the winding ll of thecut-oil relay. The removal of the receiver at substation B from itsswitch-hook causes the closure of a circuit through the supervisoryrelay &2, whereupon its armature 4:0 is attracted to open the circuitthrough the supervisory lamp Upon the replacement of either of thereceivers of the connected lines upon its switchhook the circuit throughthe associated super visory relay is opened, whereupon the supervisorylamp is caused to glow, thus indicating to the operator that thesubscriber has linished with the desired conversation. She thereuponremoves the plugs ol her cord-circuit from the line-jacks, whereupon theline-circuit apparatus is restored to its normal condition.

It will be apparent that by the arrangement of the resistances of theline and cut-oli relays as hereinbet'ore pointed out talking-current isapplied from the battery it) to the substation-transmitter through limbseach of which includes an impedance-winding of two hundred ohmsresistance. Since the batterycurrent is supplied to the transmittersthrough the apparatus of the line-circuit. it is possible to make thesupervisory relays and the supervisory controlling-relay all ofcomparatively high resistance -lor instance, live hundred ohms. It willbe seen that when the ringinggeuerator at the central station isconnected with a line a circuit is closed through the melumdred-ohmwinding of the line-relay to lock its armature in the attractedposition. The ringing-current is transmitted to the call-bell at thesubstation past an impedance-coil having a resistance of two hundredohms. It is seen that my invention provides for the necessary ordesirable impedance in both limbs of the telephone-line without theintroduction of auxiliary impedance-coils, which perform no other usefulfunction than that ol choking the voice-currents between connectedsubstations.

it is the practice in telephone systems to provide means whereby anoperator may test the condition of a line before connecting thecalling-generator therewith in order to ascertain whether such line isin use. The means provided in my improved system for such a test are asfollows: It will be seen that the test-thimbles 2+ of an idle line arepermanently com'iected, through the winding 12 ot' the cut-oil relay andthe winding H of the linerelay, with the negative pole ol the battery10. No current liowing through these windings, the test-thimbles aremaintained at the potential ot' the negative side of thehatteigv. When,however, a plug of a cord-circuit has been inserted within any one ofthe line-jacks,

a circuit is closed through the winding 14 of the line-relay, thewinding 12 of the cut-off relay, and the winding of the supervisorycontrolling-relay 35. The passage of current through this circuit to thepositive side of the battery 10 causes a drop in the potential of thetest-thimbles 24. It will be seen that the manipulation of thelistening-key to connect the operators telephone set in bridge of thecord-circuit connects the contact 45 through the impedance-coil 4:4:with the negative side of the battery 10. This of course brings the tipof the calling-plug 26 to the potential of the negative pole of thebattery 10. Thus when the tip of a calling-plug is applied to thetest-thimble of an idle line no current will be caused to flow throughthe impedancecoil H, since the test-thimble and the tip of thecalling-plug are at the same potential. WVhen, however, the potential ofthe test-thimbles has been reduced by connection with some othercord-circuit, a current will be caused to flow between the tip of thecalling-plug and the test-thimble, this current passing through theimpedance-coil 44., thereby causing a condenser-discharge which producesa click in the operators receiver, thereby notifying her of the busycondition of the tested line.

While I have herein shown and described one particular embodiment of myinvention, it will be apparent to those skilled in the art that manymodifications therein may be made without departing from the spirit ofmy invention. 1 do not, therefore, wish to limit myself to the precisedisclosure herein set forth; but,

Having described my invention, I claim as new and desire to secure byLetters Patent 1. In a telephone-exchange system, the combination with asource of current at the exchange, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, aline-relay having two cumulative windings and a cut-off relay having twodifferential windings permanently serially included in thetelephone-line circuit, a line-signal jointly controlled by said lineand cut-off relays, cord connecting apparatus for connecting said linewith another for conversation, and means whereby the connection of saidcord connecting apparatus with said line closes a circuit of decreasedresistance through one winding of said cut-off relay to cause anactuation thereof.

2. In atelephone-exchange system, the combination with a source ofcurrent at the exchange, of a telephone-line extending by its limbs fromthe terminals of said source of current to a substation, a line-relayhaving two cumulative windings and a cut-off relay having twodifferential windings serially included in the telephone-line circuit, aline signal jointly controlled by said line and cut-off relays, cordconnecting apparatus for connecting said line with another forconversation,

means whereby the connection of said cord connecting apparatus with saidline closes a circuit of decreased resistance through one winding ofsaid cut-off relay to cause an actuation thereof and switching meansadapted upon actuation of said cut-ofi relay to shortcircuit one windingthereof.

3. In atelephone-exchange system, the combination with a source ofcurrent at the exchange, of a telephone-line extending by its limbs fromthe terminals of said source of current to a substation, a line-relayhaving two cumulative windings and a cut-off relay having twodifferential windings permanently included in the telephone-linecircuit, a linesignal jointly controlled by said line and cutofi relays,cord connecting apparatus for connecting said line with another forconversation, and means whereby the connection of said cord connectingapparatus with said line closes a circuit of decreased resistancethrough one winding of said cut-oft relay to cause an actuation thereof.

4. In a telephone-exchange system, the combination with a source ofcurrent at the exchange, of a telephone-line extending by its limbs fromthe terminals of said source of current to a substation, a line-relayhaving two cumulative windings and a cut-off relay having twodifierential windings included in the telephone-line circuit, aline-signal jointly controlled by said line and cut-off relays, cordconnecting apparatus for connecting said line with another forconversation, means whereby the connection of said cord connectingapparatus with said line closes a circuit of decreased resistancethrough one winding of said cut-off relay to cause an actuation thereofand switching means adapted upon actuation of said cut-0E relay toshort-circuit one winding thereof.

5. In a telephone-exchange system, the combination with a source ofcurrent at the exchange, of a telephone-line extending by its limbs fromthe terminals of said source of cur rent to a substation, a line-relayhaving two cumulative windings and a cut-off relay having twodifferential windings permanently serially included in thetelephone-line circuit, a line-signal jointly controlled by said lineand cut-ofl relays, cord connecting apparatus for connecting said linewith another for conversation, and means whereby the connection of saidcord connecting apparatus with said line causes an actuation of saidcut-off relay to destroy the substation control of the linerelay.

6. In a telephone-exchange system, the combination with a source ofcurrent at the exchange, of a telephone-line extending by its limbs fromthe terminals of said source of current to a substation, a line-relayhaving two cumulative windings and a cut-off relay having twodifferential windings serially included in the telephone-line circuit, aline-signal 7. In atelephone-exchangesystem,the combination with asource of current at the exchange, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, aline-relay having two cumulative windings and a cut-off relay having twodifferential windings permanently included in the telephone-linecircuit, a line-signal jointly controlled by said line and cut-ofi'relays, cord connecting apparatus forconnecting said line with anotherfor conversation, and means whereby the connection of said cordconnecting apparatus with said line causes an actuation of' said cut-offrelay to destroy the substation control of the line-relay.

8. In a telephone-exchange system, the combination with a source ofcurrent at the exchange, of' a telephone-line extending by its limbsfrom the terminals of said source of current to a substation, aline-relay having two cumulative windings and a cut-off relay having twodifl'erential windings included in the telephone-line circuit, aline-signal jointly controlled by said line and cut-oti relays, cordconnecting apparatus for connecting said line with another forconversation, means whereby the connection of' said cord connectingapparatus with said line causes an actuation of said cut-off relay todestroy the substation control of the line-relay and switching meansadapted upon actuation of said cut-off relay to short-circuit onewinding thereof.

9. In a telephone-exchange system, the combination with a source ofcurrent at the exchange, of' a telephone-line extending by its limbsfrom the terminals of said source of' current to a substation, aline-relay having two cumulative windings and a cut-off relay having twodifferential windings permanently serially included in thetelephone-line circuit, a local signal-circuit jointly controlled bysaid relays, armatures for said relays adapted for serial inclusion insaid local circuit with asignal, cord connectingapparatus for connectingsaid line with another for conversation, and

means whereby the connection of said cord connecting apparatus with saidline closes a circuit of decreased resistance through one winding ofsaid cut-off relay to cause an actuation thereof.

11). In a telephone-exchange system, the combination with a source ofcurrent at the exchange, of a telephone-line extending by its limbs fromthe terminals of' said source of' current to a substation, a line-relayhaving two cumulative windings and a cut-off relay having twodifferential windings permanently serially included in thetelephone-line circuit, cord connecting appa "at-us for connecting saidline with another for conversation, and means whereby the connection ofsaid cord connecting apparatus with said line causes an actuation ofsaid cut-off relay to destroy the substation control of' the line-relay.

11. In a telephone-exchange system, the combination with a source of'current at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay permanently serially included in one limb of'said line, a second cumulative winding of' said line-relay and the twodifferential windings of a cut-off relay pern'ianently serially includedin a second limb of' said line, a line-signal jointly controlled by saidline and cut-off relays, cord connecting apparatus for connecting saidline with another for conversation, and means whereby the connection ofsaid cord connecting apparatus with said line causes an actuation ofsaid cut-ofi' relay.

12. In a telephone exchange system, the combination with a source of'current at the central station, of' a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of alinerelay serially included in one limb of' said line, asecond cumulative winding of said line-relay and the two ditlerentialwindings of a cutoff relay permanently serially included in a secondlimb of said line, a line-signal jointly controlled by said line andcutofi' relays, cord connecting apparatus for connecting said line withanother for conversation, and means whereby the connection of' said cordconnecting apparatus with said line causes an actuation of said cut-ofi'relay.

13. In a telephone-exchange system, the combination with a source of'current at the central station, of a telephone-line extending by itslimbs from the terminals of' said source of current to a substation, awinding of a linerelay permanently serially included in one limb of saidline, a second cumulative winding of said line-relay and the twodifferential windings of a cut-off relay serially included in a secondlimb of said line, a line-signal jointly controlled by said line andcut-off relays, cord connecting apparatus for connecting said line withanother for conversation, and means whereby the connection of' said cordconnecting apparatus with said line causes an actuation of said cut-otf'relay.

1%. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding ofa linerelay serially included in one limb of' said line, asecond cumulative winding of said line-relay and the two differentialwindings ofa cutofi' relay serially included in a second limb of saidTIO line, a line-signal jointly controlled by said line and cut-ofirelays, cord connecting apparatus for connecting said line with anotherfor conversation, and means whereby the connection of said cordconnecting apparatus with said line causes an actuation of said cut-offrelay.

15. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line, asecond cumulative winding of said line-relay and the t vo differentialwindings of a cut-ofl' relay serially included in a second limb of saidline, a line-signal jointly controlled by said line and cut-off relays,cord connecting apparatus for connecting said line with another forconversation, and means whereby the connection of said cord connectingapparatus with said line closes a circuit of decreased resistancethrough one winding of said cut-off relay, whereby the same is actuatedto destroy the substation control of the line-signal.

16. In a telephone-exchange system, the combination with a source ofcurrent at the' central station, of a telephone-line extending by itslimbs from the terminals of said source of current to asubstation, awinding of a linerelay permanently serially included in one limb of saidline, a second cumulative winding of said line-relay and the two'differential windings of a cut-off relay permanently serially includedin a second limb of said line, a local signal-circuit jointly controlledby said relays, armatures for said relays adapted for serial inclusion'in said local circuit with a signal, cord connecting apparatusforconnecting said line with another for conversation, and means wherebythe connection of said cord connecting apparatus with said line causesan actuation of said cut-ofl' relay.

1?. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line, asecond cumulative winding of said linerelay and the two difi'erentialwindings of a cutofl:' relay permanently serially included in a secondlimb of said line, a local signal-circuit jointly controlled by saidrelays, armatures for said relays adapted for serial inclusion in saidlocal circuit with a signal, cord connecting apparatus for connectingsaid line with another for conversation, and means whereby theconnection of said cord connecting apparatus with said line causes anactuation of said cut-off relay.

18. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay permanently serially included in one limb of saidline, a second cumulative winding of said line-relay and the twodifferential windings of a cut-off relay serially included in a secondlimb of said line, a local signalcircuit jointly controlled by saidrelays, armatures for said relays adapted for serial inclusion in saidlocal circuit with a signal, cord connecting apparatus for connectingsaid line with another for conversation, and means whereby theconnection of said cord connecting apparatus with said line causes anactuation of said cut-off relay.

19. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line, asecond cumulative winding of said line relay and the two differentialwindings of a cut-off relayserially included in a second limb of saidline, a local signal-circuit jointly controlled by said relays,armatures for said relays adapted for serial inclusion in said localcircuit with a signaL'cord connecting apparatus for connecting said linewith another for conversation, and means whereby the connection of saidcord connecting apparatus with said line causes an actuation of saidcut-off relay.

20. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of atelephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line, asecond cumulative winding of said line-relay and the two differentialwindings of a cutofi' relay serially included ina second limb of saidline, a local signal-circuit jointly controlled by said relays,armatures for said relays adapted for serial inclusion in said localcircuit with a signal, cord connecting apparatus for connecting saidline with another for conversation, and means whereby the con seriallyincluded in the telephone-line cir' cuit, a line-signal jointlycontrolled by said line and cut-ofi' relays, cord connecting apparatusfor connecting said line with another for conversation, means wherebythe connection of said cord connecting apparatus with said line closes acircuit of decreased resistance through one winding of said cut-ofi'relay to cause an actuation thereof, and switching means adapted upon anactuation of said cut-otl relay to close a low-resistance path in shuntof one winding of said cut-ott' relay.

In a telephone-exchange system, the combination with a source of currentat the exchange. of a telephone-line extending by its limbs from thetcrminalsot' said source of current to a substation, a line-relay havingtwo cumulative windings and a cut-off relay having two ditlerentialwindings included in the telephone-line circuit, a local line-signalcircuit jointly controlled by said line and cutolt' relays. armaturesfor said relays adapted tor serial inclusion in said local circuit witha line-signal.cord connectingapparatus t'orconnecting said line withanother for conversation. means whereby the connection of said cordconnecting apparatus with said line closes a circuit of decreasedresistance through one winding of said cut-otl' relay to cause anactuation thereof, and switching means adapted upon an actuation of saidcut-ott' relay to close a low-resistance path in shunt of one winding ofsaid cut-olt' relay.

2; In a telephone-exchange system, the combination with a source ofcurrent at the exchange. of a telephone-line extending by its limbs fromthe terminals of said source of current to a substation, a line-relayhaving two cumulative windings and a cut-otl' relay having twodifferential windings permanently serially included in thetelephone-line circuit, a line-signal jointly controlled by said lineand cut-otl' relays, cord connecting apparatus for connecting said linewith another for conversation, means whereby the connection of said cordconnecting apparatus with said line causes an actuation of said cut-otl'relay to destroy the substation control of the line-relay, and switchingmeans adapted upon an actuation of said cut-ott' relay to close alow-resistance path in shunt of one winding of said cutotl' relay.

2%. In a telephone-exchange system, the combination with a source ofcurrent at the exchange, of a telephone-line extending by its limbs fromthe terminals of said source of current to a substation, a line-relayhaving two tannulative windings and a cut-off relay having twoditlerential windings included in the telephone-line circuit. a localline-signal circuit jointly controlled by said line and cut-0t? relays,armatures for said relays adapted for serial inclusion in said localcircuit with a linesignal, cord connecting apparatus for connecting saidline with another for conversation. means whereby the connection of said1 line I cord connecting apparatus with said ance path in shunt of onewinding of said cutoff relay.

25. In a tclephone-exchange system, the combination with a source ofcurrent at the exchange, of a telephone-line extending by its limbs fromthe terminals of said source of current to a substation, a line-relayhaving two cumulative windings and a cuteotl' relay having twoditt'erential windings permanently se rially included in thetelephone-line circuit, a local signal-circuit jointly controlled bysaid relays, armatures for said relays adapted for serial inclusion insaid local circuit with a signal, cord connectingapparatus forconnecting said line with another For conversation, means whereby theconnection of said cord connecting apparatus with said line closes acircuit of decreased resistance through one winding of said cut-otfrelay to cause an actuation thereof, and switching means adapted upon anactuation of said cut-olf relay to close a low-resistance path in shuntof one winding of said cut-ofi relay.

26. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay permanently serially included in one limb of saidline, a second cun'iulative winding of said line-relay and the twoditt'erential windings ot' a cut-olt' relay permanently scriallyincluded in a second limb of said line, a line-signal jointly controlledby said line and cut-01f relays, cord connectingapparatus for connectingsaid line with another for conversation, means whereby the connection ofsaid cord connecting apparatus with said line causes an actuation ofsaid cut-ol'l relay, and switching means adapted upon an actuation ofsaid cut-otl' relay to close a low-resistance path in shunt ol onewinding of said cut-oll' relay.

2?. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line, asecondcumulative winding of said line-relay and the two ditferentialwindings ot a cut-oil relay permanently serially included in a sec ondlimb of said line, a line-signal jointly controlled by said line andcut-ott' relays, cord connecting apparatus t'or connecting said linewith another for conversation, means whereby the connection of said cordconnecting apparatus with said line causes an actuation of said cut-otl'relay, and switching means adapted upon an actuation of said cut-ott'relay to close a low-resistance path in shunt of one winding of saidcutott' relay.

28. In a telephone-exchange system, the combination with a source olcurrentat the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, aWinding of a linerelay permanently serially included in one limb of saidline, a second cumulative winding of said line-relay and the twodifferential windversation, and meanswhereby the connecings of a cut-offrelay serially included in a second limb of said line, a line-signaljointly controlled by said line and cut-ofl' relays, cord connectingapparatus for connecting said line witl another for conversation, meanswhereby the connection of said cord connecting apparatus with said linecauses an actuation of said cut-off relay, and switching mechanismadapted upon an actuation of said cut-ofi relay to close alow-resistance path in shunt of one winding of said cut-off relay.

29. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line, asecond cumulative winding of said line-relay and the two difl'erentialwindings of a cut-off relay serially included in a second limb of saidline, a line-signal jointly controlled by said line and cut-ofi relays,cord connecting apparatus for connecting said line with another forconversation, means whereby the connection of said cord connectingapparatus with said line causes an actuation of said cut-off relay, andswitching means adapted upon an actuation of said cut-ofl relay to closea low-resistance path in shunt of one winding of said cutofi relay.

30. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line, asecond cumulative winding of said line-relay and the two differentialwindings of a cut-01f relay serially included in a second limb of saidline, a line-signal jointly controlled by said line and cut-off relays,cord connecting apparatus for connecting said line with another forconversation, means whereby the connection of said cord connectingapparatus with said line closes a circuit of decreased resistancethrough one winding of said cut-ofi' relay, whereby the same is actuatedto destroy the substation control of the line signal, and switchingmeans adapted upon an actuation of said cut-ofl relay to close alow-resistance path in shunt of one winding of said cut-off relay.

31. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay permanently serially included in one limb of saidline, a second cumulative winding of said line-relay and the twodifijerential windings of a cut-off relay permanently serially includedin a second limb of said line, a line-signal jointly controlled by saidline and cut-off relays, cord connecting apparatus for connecting saidline with another for contion of said cord connecting apparatus withsaid line causes an actuation of said cut-off relay, the resistance ofeach winding of said cut-off relay and the resistance of said secondwinding of said line-relay being each substantially equal to one-halfthe resistance of said first winding of said line-relay.

32. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a line-relay serially included in one limb of said line, asecond cumulative winding of said linerelay and the two differentialwindings of a cut-off relay permanently serially included in a secondlimb of saidline, a line-signaljointly controlled by said line andcut-ofl' relays, cord connecting apparatus for connecting said line withanother for conversation, and means whereby the connection of said cordconnecting apparatus with said line causes an actuation of said cut-ofirelay, the resistance of each winding of said cut-off relay and theresistance of said second winding of said linerelay being eachsubstantially equal to onehalf the resistance of said first winding ofsaid line-relay.

33. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay permanently serially included in one limb of saidline, a second cumulative winding of said line-relay and the twodifferential windings of a cut-off relay serially included in a secondlimb of said line, a line-signal jointly controlled by said line andcut-off relays, cord connecting apparatus for connecting said line withanother for conversation, and means whereby the connection of said cordconnecting apparatus with said line causes an actuation of said cut-offrelay, the resistance of each winding of said cut-off relay and theresistance of said second winding of said line-relay being eachsubstantially equal to one-h-alf the resistance of said first winding ofsaid line-relay.

34:. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line, asecond cumulative winding of said line-relay and the two diiierentialwindings of a cutoff relay serially included in a second limb of saidline, a line-signal jointly controlled by said line and cut-ofi' relays,cord connecting apparatus for connecting said line with another forconversation, and means whereby the connection of said cord connectingapparatus with said line causes an actuation of said cut-otl' relay, theresistance of each winding of said cutoil relay and the resistance ofsaid second winding of said line-relay being each substantially equal toone-half the resistance of said tirst winding of said line-relay.

35. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line, asecond cumulative winding of said line-relay and the two differentialwindings of a cuto'tl' relay serially included in a second limb of saidline, a line-signal jointly controlled by said line and cut-ofi' relays,cord connecting apparatus for connecting said line with another forconversation, and means whereby the connection of said cord connectingapparatus with said line closes a circuit of decreased resistancethrough one winding of said cut-off relay, whereby the same is actuatedto destroy the substation control of the line-relay, the resistance ofeach winding of said cut-off relay and the resistance of said secondwinding of said line-relay being each substantially equal to one-halfthe resistance of said first winding of said line-relay.

36. In a telephone-exchange system, the combination with a source ofcurrent at the exchange, of a telephone-line extending by its limbs fromthe terminals of said source of current to a substation, a line-relayhaving two cumulative windings and a cut-off relay having twodifferential windings permanently serially included in thetelephone-line circuit, cord connecting apparatus for connecting saidline with another for conversation, means whereby the connection of saidcord connecting apparatus with said line closes a circuit of decreasedresistance through one winding of said cut-ofi' relay to cause anactuation thereof, and switching means adapted upon an actuation of saidcut-oil relay to close a low-resistance path in shunt of one winding ofsaid cut-oil relay, the resistance of each winding of said cut-ofl'relay and the resistance of said second winding of said line-relay beingeach substantially equal to one-half the resistance of said firstwinding of said linerelay.

37. In a telephone-exchange system. the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay permanently serially included in one limb of saidline, a second cumulative winding of said line-relay and the twodifferential windings of a cut-ofi' relay permanently serially includedin a second limb of said line, a line-signal jointly controlled by saidline and cut-otl relays, cord connecting apparatus for connecting saidline with another for conversation, means whereby the connection of saidcord connecting apparatus with said line causes an actuation of saidcut-off relay, and switching means adapted upon an actuation of saidcut-ofl' relay to close a low-resistance path in shunt of one winding ofsaid cut-ofi relay, the resistance of each winding of said cut-off relayand the resistance of said second winding of said line-relay being eachsubstantially equal to one-half the resistance of said first winding ofsaid line-relay.

38. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line, asecond cumulative winding of said linerelay and the two differentialwindings of a cut-ofi' relay permanently serially included in a secondlimb of said line, a line-signal jointly controlled by said line andcut-off relays, cord connecting apparatus for connectingsaid line withanother for conversation, means whereby the connection of said cordconnecting apparatus with said line causes an actuation of said cut-offrelay, and switching means adapted upon an actuation of said cut-ofi'relay to close a low-resistance path in shunt of one winding of saidcut-ofi' relay, the resistance of each winding of said cut-off relay andthe resistance of said second winding of said line-relay being eachsubstantially equal to one-half the resistance of said first winding ofsaid line-relay.

39. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay permanently serially included in one limb of saidline, a second cumulative winding of said line-relay and the twodifferential windings of a cut-ofi relay serially included in a secondlimb of said line, a line-signal jointly controlled by said line andcut-oil relays, cord connecting apparatus for connecting said line withanother for conversation, means whereby the connection of said cordconnecting apparatus with said line causes an actuation of said cut-ofl'relay, and switching mechanism adapted upon an actuation of said cut-oilrelay to close a low-resistance path in shunt of one winding of saidcut-off relay, the resistance of each winding of said cut-ofi' relay andthe resistance of said second winding of said line-relay being eachsubstantially equal to one-half the resistance of said first winding ofsaid line-relay.

40. In a telephone-exchange system, the combination with a source ofcurrent at the IOC central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line, asecond cumulative winding of said linerelay and the two differentialwindings of a cut-off relay serially included in a second limb of saidline, a line-signal jointly controlled by said line and cut-ofi' relays,cord connecting apparatus for connecting said line with another forconversation, means whereby the connection of said cord connectingapparatus with said line causes an actuation of said cutoff relay, andswitching means adapted upon an actuation of said cut-E relay to close alow-resistance path in shunt of one winding of said cut-off relay, theresistance of each Winding of said cut-ofi' relay and the resistance ofsaid second Winding of said line-relay being each substantially equal toone-half the resistance of said first winding of said line-relay.

&1. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line, asecond cumulative winding of said linerelay and the two ditferentialwindings of a cut-oif relay serially included in a second limb of saidline, a line-signal jointly controlled by said line and cut-off relays,cord connecting apparatus for connecting said line with another forconversation, means whereby the connection of said cord connectingapparatus with said line closes a circuit of decreased resistancethrough one winding of said cut-off relay, whereby the same is actuatedto destroy the substation control of the line-relay, and switching meansadapted upon an actuation of said cut-off relay to close alow-resistance path in shunt of one winding of said cut-off relay,

, the resistance of each winding of said cut-on.

relay and the resistance of said second winding of said line relay beingeach substantially equal to one-half the resistance of said firstwinding of said line-relay.

12. 1n a telephone-exchange system, the combination with a source ofcurrent at the exchange, of a telephone-line extending by its limbs fromthe terminals of said source of current to a substation, a line-relayhaving two cumulative windings and a cut-off relay having twodifierential windings permanently included in the telephone-linecircuit, a line-signal jointly controlled by said line and cut-ofl'relays, cord connecting apparatus for connect- 7 ing said line withanother for conversation, a spring-jack having a test-contactpermanently connected with the common terminal of the two windings ofsaid differential cut-off relay, and means whereby the connection ofsaid cord connectingapparatus with said line closes a circuit ofdecreased resistance through one winding of said cut-oil relay to causean actuation thereof.

43. In a telephone-exchange system, the combination with a source ofcurrent at the exchange,'of a telephone-line extending by its limbs fromthe terminals of said source of current to a substation, a line-relayhaving two cumulative windings and a cut-off relay having twodiiierential windings permanently included in the telephone-linecircuit, a linesignal jointly controlled by said line and cutoff relays,cord connecting apparatus for connecting said line with another forconversation, a spring-jack having a test-contact permanently connectedwith the common terminal of the two windings of said difierentialcut-01f relay, and means whereby the connection of said cord connectingapparatus with said line causes an actuation of said cut-off relay todestroy the substation control of the line-relay.

44. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay permanently serially included in one limb of saidline, a second cumulative winding of said line-relay and the twodifierential windings of a cut-ofl? relay permanently serially includedin a second limb of said line, a line-signal jointly controlled by saidline and cut-off relays, cord connecting apparatus for connecting saidline with another for conversation, a spring-jack having a contactpermanently directly connected with the first limb of said line and atest-contact permanently connected with the common terminal of the twodifferential windings of said cut-off relay, and means whereby theconnection of said cord connecting apparatus with said line causes anactuation of said cut-off relay.

45. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line,asecond cumulative winding of said line-relay and the two differentialwindings of a cut-off relay permanently serially included in a secondlimb of said line, a line-signal jointly controlled by said line andcut-off relays, cord connecting apparatus for connecting said line withanother for conversation, a spring-jack having a contact permanentlydirectly connected with the first limb of said line and a test-contactpermanently connected with the common terminal of the two differentialwindings of said cut-off relay, and means whereby the connection of saidcord connecting apparatus with said line causes an actuation of saidcut-oft relay.

46. In a telephone-exchange system, the

combination with a source of current at the central station, of atelephone-line extending by its limbs from the terminals of said sourceof current to a substation, a winding of a linerelay permanentlyserially included in one limb of said line, a second cumulative windingof said line-relay and the two differential w indings of a cut-oti relayserially included in a second limb of said line, a line-signal jointlycontrolled by said line and cutott' relays, cord connecting apparatusfor connecting said line with another for conversation, a spring-jackhaving a contact permanently directly connect- 1 ed with the first limbof said line and a test-conl tact permanently connected with the commonterminal of the two di tlerential windings of said cut-ofi' relay, andmeans whereby the connection of said cord connecting apparatus with saidline causes an actuation of said cut-ofi relay.

U. in a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line, asecond cumulative winding of said line-relay and the two ditierentialwindings of a cutofi' relay serially included in a second limb of saidline, a line-signal jointly controlled by said line and cut-off relays,cord connecting apparatus for connecting said line with another t'orconversation, a spring-jack having a contact permanently directlyconnected with the first limb of said line and a test-contactpermanently connected with the common terminal ot' the two differentialwindings of said cut-ott relay, and means whereby the connection of saidcord connecting apparatus with said line causes an actuation of saidcut-otl relay.

as. In a telephone exchange system, the combination with a source ofcurrent at the central station, of a telephoneline extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line, asecond cumulative winding of said line-relay and the two ditferentialwindings ot' acutotf relay serially included in a second limb of saidline, a line-signal jointly controlled by said line and cut-otl' relays,cord connecting apparatus for connecting said line with another t'orconversation, a spring-jack having a contact permanentlydirectlyconnected with the first limb of said line and a test-contactpermanently connected with the common terminal of the two difl'erentialwindings ofsaid cut-otl relay, and means whereby the connection of saidcord connecting apparatus with said line closes a circuit of decreasedresistance through one winding of said cut-otl' relay, whereby the sameis actuated to destroy the substation control of the line-signal.

49. In a telephone-exchange system, the combination with a source olcurrent at the central station, of a telephone-line extending by itslimbs from the terminals ol said source of current to a substation. awii'idingot' a linerelay permanently serially included in one limb ofsaid line, a second cumulative windingot said line-relay and the twoditlerential windings of the cut-off relay permanently serially includedin a second limb of said line, a line-signal jointly controlled by saidline and cut-ofl' relays, cord connecting apparatus for connecting saidline with another for conversation, a spring-jack having a contactpermanently directly connected with the first limb of said line and atest-contact permanently connected with the common terminal of the twodifferential windings of said cut-off relay, means whereby theconnection of said cord connecting apparatus with said line causes anactuation of said cut-ofi' relay, and switching means adapted upon anactuation of said cutoff relay to close a low-resistance path in shuntof one winding of said cut-ofi' relay.

50. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line, asecond cumulative winding of said line-relay and the two ditferentialwindings of a eut-oti relay permanentlyserially included in a secondlimb of said line, a line-signal jointly controlled by said line andcut-otl relays, cord connecting apparatus for connecting said line withanother for conversation, a spring-jack having a contact permanentlydirectly connected with the first limb of said line and a testeontaetpermanently connected with the common terminal of the two differentialwindings of said cut-off relay, means whereby the connection of saidcord connecting apparatus with said line causes an actuation of saidcut-otf relay, and switching means adapted upon an actuation of saidcut-off relay to close a low-resistance path in shunt of one winding ofsaid cut-off relay.

51. In a telephone-exchange system, the

combination with a source of current at the central station, of atelephoneline extending by its limbs from the terminals of said sourceof current to a substation, a winding of a linerelay permanentlyserially included in one limb of said line, a second cumulative windingof said line-relay and the two dillerential windings of a cut-off relayserially included in a second limb of said line, a line-signal jointlycontrolled by said line and cut-otf relays, cord connecting apparatusfor connecting said line with another for conversation, a spring-jackhaving a contact permanently directly connected with the first limb ofsaid line and a test-contact permanently connected with the commonterminal of the two differential windings of said cut-ofi relay, meanswhereby the connection of said cord connecting apparatus with said linecauses an actuation of said cut-off relay, and switching mechanismadapted upon an actuation of said cutoff relay to close a low-resistancepath in shunt of one winding of said cut-01f relay.

52. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line, asecond cumulative winding of said line-relay and the two differentialwindings of a cut-off relay serially included in a second limb of saidline, a line-signal jointly controlled by said line and cut-off relays,cord connecting apparatus for connecting said line with another forconversation, a spring-jack having a contact permanently directlyconnected with the first limb of said line and a test-contactpermanently connected with the common terminal of the two differentialwindings of said cut-ofi relay, means whereby the connection of saidcord connecting apparatus with said line causes an actuation of saidcut-elf relay, and switching means adapted upon an actuation of saidcut-off relay to close a low-resistance path in shunt of one winding ofsaid outoff relay.

53. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line, asecond cumulative winding of said line-relay and the two diflierentialwindings of a cut-off relay serially included in a second limb of saidline, a line-signal jointly controlled by said line and cut-ofli'relays, cord connecting apparatus for connecting said line with anotherfor conversation, a spring-jack having a contact permanently directlyconnected with the first limb of said line and a test-contactpermanently connected with the common terminal of the two dilferentialwindings of said cut-off relay, means whereby the connection of saidcord connecting apparatus with said line closes a circuit of decreasedresistance through one winding of said cut-01f relay, whereby the sameis actuated to destroy the substation control of the line-signal, andswitching means adapted upon an actuation of said cut-off relay to closea low-resistance path in shunt of one winding of said cut-off relay.

54:. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awindingof a linerelay serially included in one limb of said line,

a second cumulative winding of said line-relay and the two diflerentialwindings of a cut-off relay serially included in a second limb of saidline, a line-signal jointly controlled by said line and cut-off relays,cord connecting apparatus for connecting said line with another forconversation, a spring-jack having a contact permanently directlyconnected with the first limb of said line and a test-contactpermanently connected with the common terminal of the two differentialwindings of said cut-01f relay, and means whereby the connection of saidcord connecting apparatus with said line closes a circuit of decreasedresistance through one winding of said cut-ofl' relay, whereby the sameis actuated to destroy the substation control of the line-relay, theresistance of each winding of said cut-0E relay and the resistance ofsaid second winding of said line-relay being each substantially equal toone-half the resistance of said first winding of said linerelay.

55. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of alinerelay permanently serially included in one limb of saidline, a second cumulative Winding of said line-relay and the twodifferential windings of a cut-0H relay permanently s e rially includedin a second limb of said line, a line-signal jointly controlled by saidline and cut-off relays, cord connecting apparatus for connecting saidline with another for conversation, a spring-jack having a contactpermanently directly connected with the first limb of said line and atest-contact permanently connected with the common terminal of the twodifferential windings of said cut-off relay, means whereby theconnection of said cord connecting apparatus with said line causes anactuation of said cut-ofi relay, and switching means adapted upon anactuation of said cutofl relay to close a low-resistance path in shuntof one winding of said cut-01f relay, the resistance of each winding ofsaid cut-off relay and the resistance of said second winding of saidline-relay being each substantially equal to one-half the resistance ofsaid first winding of said line-relay.

56. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in one limb of said line, asecond cumulative winding of said line-relay and the two difierentialwindings of a cutoil relay permanently serially included in a secondlimb of said line, a line-signal jointly controlled by said line andcut-off relays, cord connecting apparatus for connecting said line withanother for conversation, at spring-jack having a contact permanentlydirectly connected with the first limb of said line and a test-contactpermanently connected with the common terminal of the two differentialwindings of said cut-oti' relay, means whereby the connection of saidcord connecting apparatus with said line causes an actuation of saidcutofi' relay, and switching means adapted upon an actuation of saideut-ofi relay to close a low-resistance path in shunt of one winding ofsaid cut-ofi relay, the resistance of each winding of said cut-ofl relayand the resist ance of said'second winding of said line-relay being eachsubstantially equal to one-half the resistance of said lirst winding ofsaid linerelay.

57. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay permanently serially included in one limb of saidline, a second cumulative winding of said line-relay and the twodifferential windings of a cutofi relay serially included in a secondlimb of said line, a line-signal jointly controlled by said line andcut-ofl' relays, cord connecting apparatus for connecting said line withanother for conversation, a spring-jack having a contact permanentlydirectly connected with the first limb of said line and a test-contactpermanently connected with the common terminal of the two differentialwindings of said cut-off relay, means whereby the connection of saidcord connecting apparatus with said line causes an actuation of saidcut-ofi' relay, and switching mechanism adapted upon an actuation ofsaid outofi relay to close a low-resistance path in shunt of one windingof said cut-ofi relay, the resistance of each winding of said cut-offrelay and the resistance of said second winding of said line-relay beingeach substantially equal to one-half the resistance of said firstwinding of said line-relay.

58. In a telephone-exchange system, the combination with a source ofcurrent at the central station, of a telephone-line extending by itslimbs from the terminals of said source of current to a substation, awinding of a linerelay serially included in onelimb of said line, asecond cumulative winding of said line-relay and the two difi'erentialwindings of a cut-off relay serially included in a second limb of saidline, a line-signal jointly controlled by said line and cut-ofl' relays,cord connecting apparatus for connecting said line with another forconversation, a spring-jack having a contact permanently directlyconnected with the first limb of said line and a test-contactpermanently connected with the common terminal of the two differentialwindings of said cutoff relay, means whereby the connection of said cordconnecting apparatus with said line causes an actuation of said cut-01frelay, and switching means adapted upon an actuation of said cut-ofi'relay to close a low-resistance path in shunt of one winding of saidcut-otl' relay, the resistance of each winding of said cut-off relay andthe resistance of said second winding of said line-relay being eachsubstantially equal to one-half the resistance of said first winding ofsaid line-relay.

59. In a telephone-exchange system, the combination with a source ofcurrent at a central exchange, of a substation permanently connectedtherewith through the line-limbs, a line-relay having two windings onepermanently included in each limb, and a cut-ofi relay for controllingsaid line-relay having two windings permanently included serially in onelimb with the line-relay winding therein, the joint impedance of thewindings in one limb being substantially equal to the impedance of thewinding in the other limb.

60. In a telephone-exchange system, the combination with a source ofcurrent at the exchange, of a telephone-line extending by its limbs fromthe terminals of said source of current to a substation, a line-relayhaving two cumulative windings and a cut-0d relay having twodifferential windings permanently serially included in thetelephone-line circuit, cord connectingapparatus for connectingsaid linewith another for conversation, a springjack having a contact permanentlydirectly connected with one limb of said line and a test-contactpermanently connected with the common terminal of the two difi'erentialwindings of said cut-ofi' relay, means whereby the connection of saidcord connecting apparatus with said line closes a circuit of decreasedresistance through one winding of said cut-off relay to cause anactuation thereof, and switching means adapted upon an actuation of saidcut-ofi relay to close a low-resistance path in shunt of one winding ofsaid cut-ol'l' relay.

61. In a telephone-exchange system, the combination with a source ofcurrent at the exchange, of a telephone-line extending by its limbs fromthe terminals of said source of current to a substation, a line-relayhaving two cumulative windings and a cut-off relay having twodifi'erential windings permanently serially included in thetelephone-line circuit, cord connecting apparatus for connecting saidline with another for conversation, a springjacl: having a contactpermanently directly connected with one limb of said line and atest-contact permanently connected with the common terminal of the twodifferential windings of said cut-off relay, means whereby theconnection of said cord connecting apparatus with said line closes acircuit of decreased resistance through one winding of said cut-ofi'relay to cause an actuation thereof, and switching means adapted upon anactuation of said cut-ofl' relay to close a low-resistance path in shuntof one Winding of said cut-ofi relay, the resistance of each Winding ofsaid cut-off relay and the resistance of said second Winding of saidline-relay being each substantially equal to one-half the resistance ofsaid first Winding of said line-relay.

In Witness whereof I hereunto subscribe my name this 5th day ofFebruary, A. D. 1903.

HARRY G. WEBSTER.

Witnesses:

LYNN A. VVILLIAMS, HARVEY L. HANSON.

